1. Field of the Invention
This invention relates to a photographic color couplers and, more particularly, to novel 2-equivalent cyan couplers, color photographic light-sensitive materials containing said couplers, and image-forming processes using said couplers.
2. Description of the Prior Art
It is well known that when an imagewise exposed silver halide photographic light-sensitive material is subjected to color development processing, an oxidation product of the aromatic primary amine developing agent reacts with a dye-forming coupler to form a color image.
Usually, a color-reproducing process based on subtractive color photography is relied upon, forming cyan, magenta, and yellow color images, the colors of which are in complementary relation with red, green, and blue, respectively. For example, phenolic derivatives or naphtholic derivatives are used as couplers for forming cyan color images.
In color photography, color-forming couplers are added to a developer or incorporated in a light-sensitive photographic emulsion layer or other color image-forming layer and, when reacted with an oxidation product of a color-developing agent formed upon development, they form non-diffusing dyes. The reaction between the coupler and the color-developing agent proceeds at the active site (also referred to as the "coupling active position") of the coupler. Couplers having a hydrogen atom substituted at this active site or position are 4-equivalent couplers, which theoretically require 4 mols of silver halide with a developing center (i.e., exposed silver halide) as an oxidizing agent for forming 1 mol of a dye. On the other hand, couplers having at the active site a group capable of being eliminated as an anion (i.e., a "coupling-off" group) are 2-equivalent couplers, which require only 2 mols of silver halide with a developing center as an oxidizing agent for forming 1 mol of dye. Therefore, they generally permit a reduction in the amount of silver halide incorporated in a light-sensitive layer and in the thickness of the film, thus enabling shortening of the time for processing light-sensitive materials and improving sharpness of color images formed. As examples of coupling-off groups (also known as eliminatable groups), U.S. Pat. No. 3,737,316 describes a sulfonamido group, U.S. Pat. No. 3,749,735 describes an imido group, U.S. Pat. No. 3,622,328 describes a sulfonyl group, U.S. Pat. No. 3,476,563 describes an aryloxy group, U.S. Pat. No. 3,311,476 describes an acyloxy group, and U.S. Pat. No. 3,214,437 describes a thiocyano group. Also, U.S. Pat. No. 4,032,345 describes an isothiocyanato group, U.S. Pat. No. 4,046,573 describes a sulfonyloxy group, Japanese Patent Application (OPI) No. 51939/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") describes a thiocarbonyloxy group, Japanese Patent Application (OPI) Nos. 39126/78 and 39745/78 describe an aralkenylcarbonyloxy group, Japanese Patent Application (OPI) No. 45524/78 describes an S-substituted monothiocarbonyloxy group, Japanese Patent Application (OPI) No. 47827/78 describes a propioloyloxy group, U.S. Pat. No. 4,072,525 describes a group of ##STR1## and U.S. Pat. Nos. 3,227,551 and 4,052,212, Japanese Patent Application (OPI) Nos. 120334/75, 18315/77, 90932/77, 52423/78, 99938/78, 105226/78, 14736/79 and 48237/79 describe substituted alkoxy groups.
Proper selection of such coupling-off groups (for example, selection of a group having a diffusible dye moiety) permits the use of the couplers in a diffusion transfer process, wherein images of diffusible dyes are formed in an image-receiving layer. Such couplers are called diffusible dye-releasing (DDR) couplers and are described, for example, in U.S. Pat. Nos. 3,227,550, 3,765,886, U.S. Defensive Publication No. T 900,029, British Pat. No. 1,330,524, and so forth. Some colored 2-equivalent couplers have a masking effect for color correction of a dye image, and examples of such colored couplers are described, for example, in Japanese Patent Application (OPI) No. 26034/76.
2-Equivalent couplers from which a development inhibiting product is eliminated are referred to as development inhibitor-releasing (DIR) couplers, and inhibit development in proportion to the amount of silver deposit, thus contributing to a reduction in image-forming particle size, adjustment of gradation, and improvement of color reproduction. In addition, they can be used in a diffusion transfer process, utilizing their inhibiting action on an adjacent layer. Examples of these couplers are described in U.S. Pat. No. 3,227,554, Japanese Patent Application (OPI) No. 122335/74, and West German Patent Application (OLS) No. 2,414,006.
2-Equivalent couplers have important advantages over 4-equivalent couplers, as described above, and have a variety of particular applications; thus, they are often used. However, many conventionally known 2-equivalent cyan-forming couplers suffer from the defects of insufficient coupling reactivity, formation of color fog, coating problems due to poor dispersibility, difficulty in storage for long periods of time due to poor stability, and poor storage stability of color images formed by color development. Thus improvements to overcome these defects have been desired.